Cutting tools capable of performing high-quality, high-efficiency cutting of workpieces are disclosed in the below-mentioned Patent documents 1 and 2.
The cutting tool disclosed in Patent document 1 is used for machining hardened steel and includes a major cutting edge which performs a major portion of the necessary cutting, and a minor cutting edge connecting with the major cutting edge to remove a affected layer formed on the surface of the workpiece by the major cutting edge and simultaneously finish the surface to required dimensions.
The cutting tool (indexable insert) disclosed in Patent document 2 includes a cutting edge for rough cutting and a cutting edge for finish cutting. The cutting edge for finish cutting removes any feed mark formed on the surface of the workpiece when the cutting edge for rough cutting is fed to cut the workpiece. Commercially available wiper inserts having wiper cutting edges also include a cutting edge for rough cutting and a cutting edge for finish cutting.
In the cutting tool disclosed in Patent document 1, the minor cutting edge, which defines an arcuate nose, removes a affected layer (also called “white etching layer”) formed on the finished surface by the major cutting edge. But in this arrangement, the shape of the minor cutting edge tends to be transferred onto the finished surface in the form of corrugated feed marks, thus detrimentally influencing the surface roughness of the finished surface. Although the surface roughness of the finished surface can be improved by reducing the depth of cut of the minor cutting edge and the feed rate of the tool, this solution will reduce the machining efficiency.
In order to improve the fatigue strength, it is desired that no affected layer be present on the finished surface of the workpiece, and that compressive stress remain on the finished surface. In this regard, the tool of Patent document 1 can scarcely apply compressive stress on the finished surface, though its minor cutting edge can remove any affected layer. Thus, if it is necessary to apply compressive stress to the surface (finished surface) of the workpiece, it is necessary to burnish the finished surface later using a burnishing tool.
The finishing cutting edge of the cutting tool disclosed in Patent document 2 and the wiper cutting edge of a commercially available wiper insert are both basically used for cutting workpieces. These cutting edges cut portions that are left uncut by the cutting edge for rough cutting, i.e. the crests of the feed marks. Thus, the finishing cutting edge and the wiper cutting edge are not cut into the workpiece, exceeding the depth of cut d of the cutting edge for rough cutting, and therefore cannot remove any affected layer. They scarcely have the burnishing function, either. Thus, if residual compressive stress is required on the surface of the workpiece, it is necessary to burnish the surface of the workpiece, as with the tool of Patent document 1.
Patent document 1: Japanese patent publication 59-42201A
Patent document 2: Japanese utility model publication 63-110304